1. Field of the Invention
The present invention relates to a method for manufacturing a capsule toner.
2. Description of the Related Art
In electrophotographic image forming apparatuses, a surface of an image bearing member is uniformly charged by a charging section (charging step), and this surface of the image bearing member is exposed by an exposure section and the charge of the exposed part is dissipated to form an electrostatic latent image (exposure step). Then, a toner which is a colored fine powder having a charge is adhered to the electrostatic latent image to make the image visible (developing step) and the obtained visible image is transferred to a recording medium such as paper (transfer step). Further, the visible image is fixed on a recording medium by applying heat and/or pressure, or other fixing methods by means of a fixing section (fixing step). By performing the steps as described above, an image is formed on the recording medium. Further, cleaning of the image bearing member is carried out in order to remove the toner which is not transferred to a recording medium and remains on the surface of the image bearing member (cleaning step).
It is necessary that the toner used for formation of these images be provided with functions required in each of a transfer step, a fixing step, and a cleaning step as well as a developing step.
Examples of the method for fixing a toner include a heat-fixing method, in which a toner is melted by applying heat and fixed on a recording medium, and a pressure-fixing method, in which a toner is plastically deformed through application of pressure to be fixed on a recording medium.
For the heat-fixing method, in consideration of the convenience of the fixing device, image quality after fixing, or the like, a heat-roll fixing method in which a heat roll is used as a heating medium for melting a toner by applying heat is often used. In this method, from the viewpoint of energy-saving, it is necessary to melt the toner at the lowest temperature possible, thereby making the toner fix on a recording medium. In this regard, low-temperature fixability of the toner is required, and reduction in the softening temperature of the toner is carried out, for example, by decreasing the molecular weight of a binder resin contained in the toner or by adding a release agent to the toner.
However, such a toner has problems of reduction in preservability since although the toner has low-temperature fixability, it is easily softened and aggregated by heat under a high temperature environment, for example, when left in a car in hot weather.
In order to solve these problems, Japanese Unexamined Patent Publication JP-A 2005-266565 discloses a toner having a core/shell structure, which contains a crystalline polyester resin in a core and an amorphous polymeric resin as a main component in a shell layer.
However, for a toner disclosed in JP-A 2005-266565, a core containing a crystalline polyester resin is covered with a shell layer including an amorphous polymeric resin, and thus, although preservability is secured, there is a problem that the low-temperature fixability of the crystalline polyester resin is deteriorated, and accordingly, both of the low-temperature fixability and the preservability are not improved together.